Since the evaluation of a thin film by ellipsometry can be utilized simultaneously to measure both the thickness and the refractive index of the file with extreme accuracy, it has various applications. For example, a monitoring method which utilizes ellipsometry in a process for forming a thin film can accurately evaluate the thickness and the composition of the film and thus has been performing an effective role in various recent semiconductor manufacturing processes required for strict accuracy. Some conventional methods of monitoring a thin film utilizing the ellipsometry are disclosed in Japanese Patent Publication Nos. 42944/74, 22912/75 and 46825/77.
The evaluation of a thin film by the ellipsometry method has been conventionally conducted heretofore after the thin film was formed on a substrate. It will be appreciated that if the ellipsometer is to be used as an in-process monitor, the thin film forming can be accurately controlled and then the effectiveness thereof may be increased. However, the ellipsometer is not yet utilized at least industrially as an in-process monitor at present. This is because the adjustment of an optical system is also difficult to associate the ellipsometer in a processor and hence an error feasibly occurs.
More specifically, in such a case, a sample holder disposed oppositely to an RF electrode in a vacuum chamber of the processor is used as a sample base for a sample to be evaluated, and a polarizer assembly and analyzer system are mounted at the position remote from the sample holder in the vacuum chamber, i.e., outside the chamber, with the result that the settlement of an incident angle and an azimuth angle (rotating angle around an optical axis) is not ready as the conventional integral ellipsometer. Consequently, when the ellipsometer is utilized by associating as a process monitor in the processor, it has such disadvantages that the adjustment of the azimuth angle is very difficult and its accuracy is wrong lack of practical utility.
Therefore, the present invention has for its object to provide a method of correcting the azimuth angle of a photometric ellipsometer capable of reducing the error of the azimuth angle by a simple way as low as possible to overcome the above-mentioned disadvantages.